1. Technical Field
Apparatuses and methods consistent with the present invention relates in general to a level shifter, and more specifically, to an ultra-low-power level shifter constituted by CMOS elements, a voltage transform circuit and an RFID (radio frequency identification) tag including the ultra-low-power level shifter.
2. Description of the Related Art
In some cases, a system needs to transform an external low voltage to a higher voltage. That is, in the case where a voltage required for driving a specific configuration of a circuit element is higher than an externally supplied voltage, it is necessary to transform the externally supplied voltage into the required driving voltage. For instance, a minimum voltage of about 15V is required for driving a nonvolatile memory, whereas an externally supplied voltage is typically about 1.5V. Therefore, in order to drive the memory, the externally supplied voltage 1.5V should be transformed to 15V.
FIG. 1 illustrates a conventional level shifter for transforming an external lower voltage signal CKin to a higher voltage signal CKout. The following description is based on this level shifter of FIG. 1.
As shown in the drawing, the level shifter receives an externally supplied power voltage Vdd and the lower voltage signal CKin, and outputs the level-shifted signal CKout. The voltage levels of Vdd and CKout satisfy the relationship shown in Equation 1 below.
                              CKout          Vdd                =        2                            [                  Equation          ⁢                                          ⁢          1                ]            
As shown in Equation 1, CKout is dependent on Vdd. That is, if Vdd is small, CKout is also small. Thus, if CKout is used as an input signal of a charge pump for generating a high voltage, the number of pumping stages of the charge pump is increased to transform an input power voltage to a required high voltage. As a result, the circuit efficiency is lowered.